1. Field of the Invention
The present invention relates to an apparatus for scanning an original. More specifically, the present invention relates to an apparatus for exposing and scanning an original provided with a lamp holder or an original table, moving along a base body, for relatively moving an original and a lamp exposing the original.
2. Description of the Prior Arts
In an apparatus for scanning an original, for example, such as an electrophotographic copy machine, normally, a mechanism for detecting a relative position of scanning means is provided. One example of a conventional original scanning apparatus is disclosed, for example, in Japanese Patent Application Laid Open No. 77243/1976 laid open on July 5, 1976 or in Japanese Utility Model Publication No. 39461/1983 published on Sept. 6, 1983.
In more detail, in the Japanese Patent Application Laid Open No. 77243/1976, for detecting four positions, a position of the original table of the electrophotographic copying machine, namely a home position, a forward going position at where the back-moving turns to the fore-moving, a starting position (a position for timing the arrangement of edges of the original and the copying paper) and a returning position at where the fore-moving turns to the back-moving, microswitches or Hall ICs corresponding to the respective positions have been used. On the other hand, in the Japanese Utility Model Publication No. 39491/1983, these positions may be estimated by counting pulse numbers of an encoder.
Thus, for detecting the position necessary for the scanning means, in the former, since a number of microswitches and the like are used, the number of components increase and result in a high cost as well as a low reliability. Also, in the latter where the encoder is used, a problem existed in that the accurate position can not be detected.